1. Field of the Invention (Technical Field)
The present invention relates to ring-constrained amino acid surrogates, methods for synthesizing ring-constrained amino acid surrogates, and methods of use of ring-constrained amino acid surrogates, including use in linear or cyclic constructs or compounds which include a plurality of amino acid residues and one or more ring-constrained amino acid surrogates.
2. Background Art
Amino Acid Surrogates. A number of different peptide mimetics are known, and are employed to make mimetics of critical function domains of peptides. See generally Bioorganic Chemistry: Peptides and Proteins, S. M. Hecht, ed., Oxford University Press, 1998, and particularly Chapter 12 thereof, pages 395-419, and the references cited therein. Peptides and proteins are highly flexible, due in large part to the high rotational degrees of freedom of individual amino acid residues. In addition, some bonds in side chains of individual amino acid residues also have rotational degrees of freedom. The non-bonded steric interactions between amino acid residues force the peptide or protein along its degrees of freedom into some stable minimal free energy configuration. Local structures, also known as a “secondary structure,” are common in peptides and proteins. These structures include α-helixes, β-bends, sheets, extended chains, loops and the like, and most often contribute to binding or receptor-specificity of peptides and proteins. There are several types of α-helixes known, differing in torsion angles within the amino acid residues of the actual turn and by the patterns of intra- and inter-molecular hydrogen bonding. There are also a number of known different β-bends, differing in the dihedral torsion angles ψ (for the Ca—C bond) or φ (for the Ca—N bond), or both. Peptide mimetics are employed to provide a conformationally restricted component in a molecule, in part with the objective of fixing critical function domains in a restricted configuration that is optimal for a desired biological response.
Typically peptide mimetics are designed and intended to fix and mimic the function of a dipeptide or tripeptide. For example, see the reverse-turn mimetics disclosed in U.S. Pat. Nos. 7,008,941, 6,943,157, 6,413,963, 6,184,223, 6,013,458 and 5,929,237, and U.S. Published Patent Application 2006/0084655, all describing various bicyclic ring structures asserted to mimic a dipeptide or tripeptide sequence. Other applications disclose a number of different small molecule compounds, again asserted to mimic a dipeptide or tripeptide sequence. See, for example, U.S. Published Patent Applications 2006/0234923 and 2003/0191049.
Natriuretic Peptide System. One potential application for amino acid surrogates employs the natriuretic peptide system, which has been extensively explored since the identification of the human atrial natriuretic peptide (ANP) sequence and gene structure in 1984. ANP is part of the natriuretic peptide system, which in humans involves an ANP gene, which through differences in post-translational processing results in both ANP and urodilatin, a gene which produces BNP, or brain natriuretic peptide, and a gene which produces CNP, or c-type natriuretic peptide. ANP, urodilatin, BNP and CNP are each ring structures, with a 17 amino acid loop formed by a cysteine-cysteine disulfide linkage. The amino acid sequence and structure of human ANP (hANP) is shown in FIG. 1. ANP, urodilatin, BNP and CNP are closely related, differing by some five or six amino acids within the ring, though the N- and C-terminal tails are substantially different.
ANP, BNP and CNP are each specific for distinct receptors, natriuretic peptide receptors A, B and C (NPRA, NPRB and NPRC). NPRA and NPRB are linked to guanylyl cyclases, while NPRC is a G-protein linked clearance receptor. ANP, BNP and CNP are the primary endogenous mammalian natriuretic peptides identified to date. However, there are a number of non-mammalian natriuretic peptides that have been identified and may have therapeutic application in mammals. These include salmon natriuretic or cardiac peptide (sCP), ventricular natriuretic peptide (VNP), a cardiac natriuretic peptide identified in eels and a variety of fish, dendroaspis natriuretic peptide (DNP), a natriuretic peptide identified in mamba snake venom, and three natriuretic-like peptides (TNP-a, TNP-b, and TNP-c) isolated from taipan snake venom. See generally Tervonen V, Ruskoaho H, Lecklin T, lives M, Vuolteenaho O, Salmon cardiac natriuretic peptide is a volume-regulating hormone. Am. J. Physiol. Endocrinol. Metab. 283:E353-61 (2002); Takei Y, Fukuzawa A, Itahara Y, Watanabe T X, Yoshizawa Kumagaye K, Nakajima K, Yasuda A, Smith M P, Duff D W, Olson K R. A new natriuretic peptide isolated from cardiac atria of trout, Oncorhynchus mykiss. FEBS Lett. 414:377-80 (1997); Schweitz H, Vigne P, Moinier D, Frelin C, Lazdunski M. A new member of the natriuretic peptide family is present in the venom of the green mamba (Dendroaspis angusticeps). J. Biol. Chem. 267:13928-32 (1992); Lisy 0, Jougasaki M, Heublein D M, Schirger J A, Chen H H, Wennberg P W, Burnett J C. Renal actions of synthetic dendroaspis natriuretic peptide. Kidney Int. 56:502-8 (1999); and Fry B G, Wickramaratana J C, Lemme S, Beuve A, Garbers D, Hodgson W C, Alewood P. Novel natriuretic peptides from the venom of the inland (Oxyuranus microlepidotus): isolation, chemical and biological characterization. Biochem. Biophys. Res. Comm. 327:1011-1015 (2005).
ANP is endogenously secreted predominately in response to increased atrial pressure, but other factors, including cytokine receptor stimulation, may contribute to endogenous secretion. Once released, ANP is a hormonal regulator of blood pressure, sodium and fluid homeostasis, providing vasorelaxant effects, affecting cardiovascular remodeling, and the like. Thus ANP, including endogenous ANP, is effective in congestive heart failure and other cardiovascular disease, in part by providing a defense against a chronically activated renin-angiotensin-aldosterone system. Circulating ANP is rapidly removed from the circulation by two mechanisms, binding to a natriuretic peptide receptor and enzymatic degradation.
Human ANP is also referred to as wild-type human ANP, hANP, ANP(1-28) and ANP(99-126) (the later referring to the relevant sequence within proANP(1-126), which is normally cleaved at Arg98-Ser99 in the C-terminal region during secretion). Hereafter human ANP is sometimes referred to as “hANP.”
In general, natriuretic peptides and variants thereof are believed to have utility in the treatment of congestive heart failure, renal hypertension, acute kidney failure and related conditions, as well as any condition, disease or syndrome for which a diuretic, natriuretic and/or vasodilatory response would have a therapeutic or preventative effect. One review article describing natriuretic peptides, including ANP, and use of the natriuretic peptide system in heart failure is Schmitt M., Cockcroft J. R., and Frenneaux M. P. Modulation of the natriuretic peptide system in heart failure: from bench to bedside? Clinical Science 105:141-160 (2003).
A large number of ANP mimetics and variations have been made, some of which are substantially reduced in size from ANP. On ANP version that is reduced in size yet is biologically active is the 15-mer disulfide cyclic peptide H-Met-cyclo(Cys-His-Phe-Gly-Gly-Arg-Met-Asp-Arg-Ile-Ser-Cys)-Tyr-Arg-NH2 (SEQ ID NO:1) as described in Li B, Tom J Y, Oare D, Yen R, Fairbrother W J, Wells J A, Cunningham B C. Minimization of a polypeptide hormone. Science 270:1657-60 (1995). This 15-mer peptide is commonly referred to as “mini-ANP”.